In the manufacture of web-like products, such as paper, textiles and plastics, a web of material is typically moved along a serpentine path during the manufacturing operation. The web moving through such a path can measure several hundred feet in length and can measure a number of feet in width. Should the web break during the manufacturing process, significant down time can occur while the web is being rethreaded. Such down time can result in substantial cost to the manufacturer as well as being detrimental to product quality if breaks occur too frequently.
One major cause of breaks is flutter. Flutter is a phenomenon in which the web moves in a direction substantially perpendicular to the direction of travel, with one or more amplitudes and frequencies. Flutter in a paper machine is generally known to be caused by two components of air flow: a cross-machine-direction component caused by large volumes of ventilated air injected into pockets between dryer cans by blow boxes to reduce humidity, and a machine-direction component represented by the laminar air flow on the web as it moves through the paper machine. As the paper moves around the dryer cans, it stretches along the center of the sheet, resulting in slack at the edges of the paper where there is less tension. This slack is susceptible to vertical motion when subjected to the multiple air flow components, and flutter develops.
Artisans have employed various foil and forced air designs for use in large scale drying and web production processes, with varying results.
King, Jr., U.S. Pat. No. 4,306,358, discloses an apparatus for air drying a slurry, such as reconstituted tobacco slurry, which is conveyed on a moveable support. The apparatus includes means for directing air flow against the supported web.
Mair, U.S. Pat. No. 4,145,796, discloses the use of a current of air for flattening the bent edges of a flexible web-type work piece, such as a textile weave or knit, synthetic resin foil or paper. The air is blown from a guide in a flow direction extending transverse to the transport direction of the work piece, outwardly from the center of the work piece. This reference illustrates a pair of converging air-directing plates for ensuring that the flattened work-piece remains flat and that the flattening effect is optimized, such as to reduce curling of the edges.
Stanley, U.S. Pat. No. 3,198,499, discloses the use of an air flow to support an advancing member during heat treatment. This reference illustrates the concept of laterally flowing a gas beneath the member in a cross-machine direction.
Andrews, U.S. Pat. No. 2,574,083, discloses the use of a baffle strip for increasing a downward air pressure against an edge of a moving web which is disposed on tenter pins in a drawing chamber.
Vits, European Patent application Ser. No. 0313806 discloses a system whereby air jets are blown in a machine direction over a moving web to stabilize the web between rolls.
While, in the main, these artisans have contributed significantly to the field of web processing, they have not provided means for efficiently reducing the amplitude and frequency of flutter in modern web handling operations. Accordingly, a need exists for a flutter suppression system which includes non-contact, low energy means for reducing the flutter of a moving web in a paper machine. Such a system should be able to employ existing cross currents of air flow and, thus, minimize energy costs while reducing the number of breaks.